Analytical Study of tlie Alternating Current Arc. 315 



Temp. 



E. 







1001-2 



- 55 



761-9 



- 65 



720-4 



- 79 



663-6 



-100 



581-0 



-130 



467-3 



-182 



291-0 



£?R (ohms per 



dT degree). 



4-65 



4-20 



4-12 



4-02 



3-87 



3-66 



The author prefers now a slightly different type of electric 

 thermometer, differing from that shown on fig. 4 in this par- 

 ticular, that the brass tube c joins the outer cylinder i J . 

 Although rather more difficult to construct, it allows the 

 resistance-coil to embrace the bulb of a hydrogen-thermo- 

 meter or any other piece of apparatus the temperature of 

 which is to be determined. 



XXXIY. An Analytical Study of the Alternating Current Arc. 

 By J. A. Fleming, M.A., D.Sc, F.R.S., Professor of 

 Electrical Engineering in University College, London, and 

 J. E. Petavel*. 



ALTHOUGH the physical phenomena of the Electric 

 Arc have received of late years very considerable 

 attention, there are many points in connexion with the study 

 of the alternating current arc which seem to us to have 

 been insufficiently explored. The investigation which is here 

 described is a contribution to the further examination of the 

 mode in which the variation of the luminous and electric 

 effects takes place in the alternating current arc. 



The first portion of the research is concerned with an 

 analytical study of the variation of the light thrown out from 

 different radiating regions in the arc, and the delineation of the 

 periodic value of this illuminating power by graphical methods. 

 The object of the first set of experiments was to record and 

 represent by an appropriate graphical method the periodic 

 value of the light thrown out from the carbons and from the 

 true electric arc region when the arc is supplied with electric 

 power of known constant amount and varying magnitude, 

 and at the same time to record the periodic variation of 

 current through the arc, and potential-difference of the 

 carbons. The instrumental appliances involved in the first 

 place the employment of means for keeping constant and 



* Communicated by the Physical Society : read February 28th, 1896. 



